1. Field of the Invention
This invention relates to a method of making a material for bearings, and more particularly to a method of making a material suitable for bearing by pressure bonding an aluminum base alloy powder to a steel strip (including a stainless steel strip) by means of hot rolling in the air.
2. Description of the Prior Art
In recent years, an aluminum-bonded steel has come into use for the fabrication of rotary, sliding and like parts of vehicles and other machines, and a variety of methods have been proposed an employed for the manufacture of such a bearing material. However, any of these conventional manufacturing methods poses a problem in the pressure bonding of a steel strip and an aluminum powder which will ultimately form the surface layer of the resulting back steel i.e. the bearing surface; hence, there is a strong demand for a solution to this problem.
In Japanese Patent Application Publications Nos. 39213/71 and 20330/64, there is disclosed such a method as shown in FIG. 1a in which an aluminum powder 2, which will ultimately form a bearing surface (which powder will therefore be hereinafter referred to as a bearing powder), is spread by a spreader 3 over the entire surface of a steel strip 1 and then pressure-bonded thereto by heat rolling between a pair of rolls 5 in a reducing furnace 4. With this method, however, an expensive reducing furnace is needed and the pair of rolls 5 must be placed in the furnace 4, so that there are serious problems in equipment and in dimensional control during rolling.
In Japanese Patent Disclosure No. 20336/77 there is set forth such a method as shown in FIG. 1b in which the bearing powder 2 is spread all over the steel strip 1 together with a binding powder such as aluminum, an aluminum base alloy or the like and the powders are pressure-bonded to the steel strip 1 by cold rolling between the pair of rolls 5 and then the resulting sheet is annealed in a heating furnace 4. With this method, however, the powders are pressure-bonded at room temperature, so that in order to achieve the pressure bonding to a certain degree (i.e. to roll the bearing powder nearly to its forging density), it is necessary to apply such a large rolling force as to reduce the thickness of the steel strip about 15%; this induces a large strain in the steel strip and is likely to introduce difficulty in the subsequent working. Further, this method cannot be used with a powder which is difficult to be sintered, such as an Al--Si--Cu--Pb--Sn alloy powder. After the pressure bonding, the aluminum-bonded steel strip is continuously annealed in the heating furnace 4 and then taken up on a reel; if this annealing is insufficient, the bearing surface layer is liable to crack.
In Japanese Patent Disclosure No. 83651/74 there is disclosed such a method as depicted in FIG. 1c in which the bearing powder 2 is spread over the entire surface of the steel strip 1 and heated in a furnace 4 containing an inert atmosphere, thereafter being rolled between the pair of rolls 5 for pressure bonding to the steel strip 1. This method involves the step of heating in the inert atmosphere, and hence requires expensive equipment as is the case with any of the aforesaid methods; furthermore, a large amount of inert gas is needed inevitably resulting in the manufacturing cost being raised.
Moreover, U.S. Pat. Nos. 3,104,135 and 3,093,885 propose such a cladding method as shown in FIG. 1d in which a bearing steel sheet 6, prefabricated by a complicated manufacturing process, is clad on a steel strip by the pair of rolls 5. This method requires expensive apparatus such as a continuous forcing machine, a powder roll machine and so forth.